Thermal processing of bulk solids

Abstract

An apparatus for drying or conditioning bulk solids, includes a housing including an inlet for receiving the bulk solids, and an outlet for discharging the bulk solids, a plurality of spaced apart heat transfer plates assemblies disposed in the housing between the inlet and the outlet for passage of the bulk solids that flow from the inlet, through spaces between the heat transfer plates, and a sweep gas delivery system for the flow of sweep gas in a first direction across the direction of flow of the bulk solids. The sweep gas delivery system includes at least one valve for reversing the flow of the sweep gas from the first direction to a second direction, opposite to the first direction.

The invention claimed is: 
     
       1. An apparatus for drying or conditioning bulk solids, the apparatus comprising:
 a housing including an inlet for receiving the bulk solids, and an outlet for discharging the bulk solids; 
 a plurality of spaced apart heat transfer plates assemblies disposed in the housing between the inlet and the outlet for passage of the bulk solids that flow from the inlet, through spaces between the heat transfer plates; 
 a sweep gas delivery system for the flow of sweep gas in a first direction across the direction of flow of the bulk solids, the sweep gas delivery system including at least one valve for reversing the flow of the sweep gas from the first direction to a second direction, opposite to the first direction. 
 
     
     
       2. The apparatus according to  claim 1 , wherein each of the heat transfer plates includes a fluid inlet and a fluid outlet for the flow of a heating fluid through the heat transfer plates. 
     
     
       3. The apparatus according to  claim 2 , wherein each of the heat transfer plates comprises a pair of metal sheets that are coupled together and include at least one passage between the metal sheets for the flow of the heating fluid through the heat transfer plates. 
     
     
       4. The apparatus according to  claim 2 , wherein the pair of metal sheets are joined together at a plurality of spaced apart locations to facilitate flow of the heating fluid through the heat transfer plate. 
     
     
       5. The apparatus according to  claim 1 , wherein the sweep gas delivery system includes a sweep gas source coupled to the at least one valve for the supply of sweep gas in the first direction through the housing and in the second direction through the housing. 
     
     
       6. The apparatus according to  claim 5 , wherein the sweep gas delivery system includes a sweep gas draw coupled to the at least one valve to draw the sweep gas out of the housing. 
     
     
       7. The apparatus according to  claim 6 , wherein the at least one valve is coupled to opposing sides of the housing for controlling flow of sweep gas through the housing. 
     
     
       8. The apparatus according to  claim 6 , wherein the at least one valve is coupled to opposing sides of the housing for controlling flow of sweep gas in the first direction in which the sweep gas flows generally from a first one of the opposing sides to a second one of the opposing sides when the at least one valve is in a first flow control configuration, and for the reversal of the direction of flow of sweep gas such that the sweep gas flow in the second direction, generally from the second one of the opposing sides to the first one of the opposing sides when the at least one valve is in a second flow configuration. 
     
     
       9. The apparatus according to  claim 8 , wherein the sweep gas delivery system includes a first sweep gas plenum having a first air pervious side at the first one of the opposing sides of the housing and coupled to the at least one valve, and a second sweep gas plenum having a second air pervious side at the second one of the opposing sides of the housing and coupled to the at least one valve. 
     
     
       10. The apparatus according to  claim 9 , wherein said first air pervious side comprises spaced apart wedge wire or louvers to inhibit the flow of bulk solids into the first sweep gas plenum and the second air pervious side comprises spaced apart wedge wire or louvers to inhibit the flow of bulk solids into the second sweep gas plenum. 
     
     
       11. The apparatus according to  claim 6 , wherein the at least one valve comprises a 4-port valve including a first port coupled to a first side of the housing, a second port coupled to a second side of the housing, opposite to the first side of the housing, a third port coupled to the sweep gas supply, and a fourth port coupled to the sweep gas draw. 
     
     
       12. The apparatus according to  claim 1 , wherein the first direction is generally parallel to the heat transfer plates for the flow of sweep gas between the heat transfer plates. 
     
     
       13. The apparatus according to  claim 1 , wherein the plurality of spaced apart heat transfer plates are arranged in banks including a first bank of spaced apart heat transfer plates disposed in the housing between the inlet and the outlet and a second bank of spaced apart heat transfer plates disposed in the housing between the first bank and the outlet. 
     
     
       14. The apparatus according to  claim 13 , wherein the sweep gas delivery system comprises a first pair of sweep gas plenums associated with the first bank to facilitate the flow of sweep gas across the direction of flow of the bulk solids as the bulk solids pass through the spaces between the heat transfer plates of the first bank and a second pair of sweep gas plenums associated with the second bank to facilitate the flow of sweep gas across the direction of flow of the bulk solids as the bulk solids pass through the spaces between the heat transfer plates of the second bank. 
     
     
       15. The apparatus according to  claim 14 , wherein the sweep gas delivery system comprises valves, at least one valve associated with respective pairs of sweep gas plenums such that each bank of heat transfer plates is associated with at least one respective valve configured to switch the direction of flow of the sweep gas between the first direction and the second direction. 
     
     
       16. A method of drying or conditioning bulk solids, the method comprising:
 introducing the bulk solids into an inlet of a housing through which the bulk solids flow through spaces between spaced apart heat transfer plates; 
 subjecting the bulk solids to heating utilizing the heat transfer plates as the bulk solids flow, by the force of gravity, through the spaces between the heat transfer plates, toward an outlet of the housing; 
 directing a sweep gas through the bulk solids as the bulk solids flow toward the outlet of the housing, the sweep gas being directed to flow in a first direction across the direction of flow of the bulk solids; 
 reversing direction of flow of the sweep gas by directing the flow of the sweep gas through the bulk solids, in a second direction opposite to the first direction, 
 wherein reversing direction of flow of the sweep gas comprises switching at least one valve to reverse the direction. 
 
     
     
       17. The method according to  claim 16 , comprising repeating directing the flow of the sweep gas in the first direction and reversing the flow of the sweep gas by directing flow in the second direction. 
     
     
       18. The method according to  claim 16 , comprising repeating directing the flow of the sweep gas in the first direction and reversing the flow of the sweep gas by directing flow in the second direction at regular intervals in time,
 wherein repeating directing the flow of the sweep gas in the first direction and reversing the flow of the sweep gas by directing flow in the second direction at regular intervals in time, comprises regularly switching the at least one valve to control the flow of the sweep gas. 
 
     
     
       19. The method according to  claim 16 , wherein subjecting the bulk solids to heating comprises passing heating fluid through the heat transfer plates, the heating fluid indirectly heating the bulk solids as the heating fluid passes within the heat transfer plates.